The delivery of therapeutic substances to mucosal surfaces has inherent difficulties due to the moist surface. This is particularly true for the mucosal surface of the eye where the washing action of the tear film removes much of the therapeutic substance. Estimates of the portion of a drug delivered by means of a topical drop range from 1 to 10% of the drug content. The remaining portion of the drug which does not penetrate or adhere to the eye is removed by tears through the lacrimal ducts where systemic absorption occurs through contact with nasal and gastro-intestinal surfaces.
A common ophthalmic problem, particularly with older people, is the condition commonly known as "dry eye" or dyslacrima. As people age, the tear ducts in the eye produce less moisture. Consequently, the eye becomes dry, inflamed and irritated.
Prior developments in the treatment of dry eye condition are described in German Patent DE 3440352 A1 and U.S. Pat. No. 3,947,573.
The German patent discloses two formulations useful in treating dry eye. The first formulation is a dry-eye solution comprising an isotonicized, water-soluble cationic cellulose derivative, and optional viscosity-enhancing additives. The second formulation comprises an acrylate-based aqueous gel containing carboxyvinyl polymers.
Despite the teachings of the prior art, there is a continuing need for a method for treating the eye in order to retain an active agent for a longer period of time.